Apparatus for measuring hematocrit

ABSTRACT

A method and apparatus for use in respect of samples which are assessed for quality prior to testing in a clinical analyzer. The method and apparatus identify parameters such as gel level and height of fluid above the gel in blood samples, where appropriate, for the purposes of positioning the specimen for determination of interferents. Such interferents include hemoglobin (Hb), total bilirubin and lipids. These interferents are determined by measurement of absorption of different wavelengths of light in serum or plasma, or other speciments, which are then compared with values obtained through calibration using reference measurements for the respective interferents in serum or plasma or other type of specimen. Determination of temperature of the specimen, as well as specimen type, for example whether the specimen is urine or plasma or serum, may also be carried out.

RELATED APPLICATION INFORMATION

This is a divisional application of U.S. patent application Ser. No.09/068,835 filed Feb. 8, 1999, now U.S. Pat. No. 6,195,158.

TECHNICAL FIELD

This invention relates to spectrophotometry and the spectrophotometricanalysis of blood samples. In particular, this invention relates to amethod and apparatus for providing a rapid pre-test determination ofinterferent concentration, specimen type and physical properties of ablood sample for a blood analyzer by measurement of absorbance orreflectance.

BACKGROUND ART

Clinical laboratory tests are routinely performed on the serum or plasmaof whole blood. In a routine assay, red blood cells are separated fromplasma by centrifugation, or red blood cells and various plasma proteinsare separated from serum by dotting prior to centrifugation.

Haemoglobin (Hb), bilirubin (Bili) and light-scattering substances likelipid particles are typical substances which will interfere with, andaffect spectrophotometric and other blood analytical measurements. Suchsubstances are referred to as interferents.

Many tests conducted on plasma or serum samples employ a series ofreactions which terminate after the generation of chromophores whichfacilitate detection by spectrophotometric measurements at one or twowavelengths. Measurement of interfering substances prior to conductingsuch tests is important in providing meaningful and accurate testresults. In fact if a sample is sufficiently contaminated withinterferents, tests are normally not conducted as the results will notbe reliable.

In analytical laboratories bar codes are increasingly being used toidentify samples, and such laboratories routinely analyze a variety ofbiologic fluids, for example, the most common being blood and urine.

Specimen integrity directly affects the accuracy of test results.Numerous factors can compromise specimen integrity such as, having theright sample, e.g., blood rather than urine; in the case of a bloodsample, whether it is serum or plasma; the presence of interferents in aplasma or serum sample; the volume of the sample; the sampletemperature; and the location of the upper surface of a gel barrier,which is also referred to herein as the gel level, in a blood sample,where the gel is an inert material used to separate serum or plasma fromclotted or packed blood bells, respectively. Finally, it is criticalthat the sample tested be properly matched to the results of anyassessments on the sample.

Current methods used for quality assurance and specimen integrity relyprincipally on visual inspection of the specimen with or withoutcomparison to a reference chart, depending upon which variable is beingassessed. Visual inspection of samples is sometimes employed on aretrospective basis where there is disagreement between test results andclinical status of the patient in order to help explain suchdiscrepancies.

A sample of plasma or serum is normally transferred from the originaltube to a secondary tube. These secondary tubes may be amber coloured toprotect photo sensitive constituents. Amber colouring makes visualinspection virtually impossible. On occasion, labels cover portions ofthe tube further restricting a full visual examination. Further, it issometimes difficult to distinguish between urine and plasma or serumsamples, even in transparent tubes.

Pre-test screening of specimens by visual inspection issemi-quantitative at best, and highly subjective and may not provide thequality assurance required.

Furthermore, visual inspection of specimens is a time consuming, ratelimiting process. Consequently, state-of-the-art blood analyzers infully and semi-automated laboratories do not employ visual inspection ofspecimens. However, other methods such as direct sampling are not rapidenough or cost effective. In order to obtain a measurement of the sampleof the plasma or serum, specimen tubes must be uncapped, a direct sampleof the specimen taken and diluted prior to measurement.

SUMMARY OF INVENTION

The disadvantages of the prior art may be overcome by providing a rapidand accurate method and apparatus for monitoring blood specimens beforesamples are presented for analysis.

In one aspect of the invention, the bar code on the specimen tube isread to identify the specimen, as well as the bar code reading,determination of the gel level of the specimen and the height of fluidabove the gel provide the basis for positioning the specimen containerso that spectral data can be obtained. The spectral data is used in anovel way to determine if the specimen which is presented for analysiscontains interferents and if so, to what extent; to determine specimentype, for example if it is urine or plasma or serum; and to determinethe temperature of the specimen.

In another aspect of the invention, there is provided an apparatus whichincorporates: A. a device to read any bar code present on a specimencontainer and thereby identify and provide information with respect topositioning the specimen; B. a device to determine the location of theupper surface of a gel barrier of the specimen and the height of fluidabove the gel; and C. A spectrophotometric device to irradiate andmeasure radiation from the specimen so as to determine if the specimenwhich is presented for analysis contains interferents and if so, to whatextent; to determine specimen type; and to determine the temperature ofthe specimen. This apparatus is capable of these determinations wherethe sample tube containing the specimen has a sample identificationlabel on the exterior surface.

In a further aspect of the invention, there is provided a method for thefollowing: to read any bar code present on specimen container andthereby identify and provide information with respect to positioning thespecimen; to determine the location of the upper surface of a gelbarrier of the specimen and the height of fluid above the gel; todetermine if the specimen which is presented for analysis containsinterferents and if so, to what extent; to determine specimen type; andto determine the temperature of the specimen. The method of thisinvention allows for these determinations where the sample tubecontaining the specimen has a sample identification label on theexterior surface.

In yet another aspect of the invention, there is provided an apparatusand a method for the determinations described herein where the radiationfrom the spectrophotometer, or other appropriate source, is transmittedthrough the label, container and specimen.

In one embodiment, the bar code reading as well as the gel level andheight of fluid above the gel are first determined. This determinationprovides information essential for proper positioning of the sample forthe following determinations. The concentration of interferents such ashemoglobin (Hb), total bilirubin (calibrated for unconjugated bilirubin,conjugated bilirubin, delta bilirubin, the sum of results for thesethree gives total bilirubin) and lipids are determined by measurement ofabsorption of different wavelengths of light in serum or plasmaspecimens which are then compared with values obtained throughcalibration using reference measurements for the respective interferentsin serum or plasma specimens. This is true also for determination oftemperature of the sample. A determination of specimen type, for examplewhether the specimen is urine or plasma or serum, is also made. Thisdetermination is made by recordal of spectral data for different samplesthen through statistical analysis, the spectra are classified accordingto sample type. In addition a bar code reading is carried out eithersimultaneously, before or after the determination of the otherparameters. To those skilled in the art, it is clear that althoughcertain sequences of determinations are outlined here, any combinationor sequence of combinations is within the scope of this invention.

In another embodiment, the bar code reading as well as the gel level andheight of fluid above the gel are first determined. This determinationprovides information essential for proper positioning of the sample forthe following determinations. The concentration of interferents such ashemoglobin (Hb), total bilirubin (calibrated for unconjugated bilirubin,conjugated bilirubin, and delta bilirubin, the sum of results for thesethree gives total bilirubin) and lipids are determined by measurement ofreflectance of different wavelengths of light in serum or plasmaspecimens which are then compared with values obtained throughcalibration using reference measurements for the respective interferentsin serum of plasma specimens. This is true also for determination oftemperature of the sample. A determination of specimen type, for examplewhether the specimen is urine or plasma or serum, is also made. Thisdetermination is made by recordal of spectral data for different samplesthen through statistical analysis, the spectra are classified accordingto sample type. In addition a bar code reading is carried out eithersimultaneously, before or after the determination of the otherparameters. To those skilled in the art, it is clear that althoughcertain sequences of determinations are outlined here, any combinationor sequence of combinations is within the scope of this invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-section of a sample holder adapted foruse with LED and radiation source.

FIG. 2 is a top view of the complete sample holder of FIG. 1.

FIG. 3 is a longitudinal cross-section of a sample holder adapted foruse with a laser and radiation source.

FIG. 4 is a top view of the complete sample holder of FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

In operation, the apparatus first conducts a determination of the barcode and its position on the tube, and, based on the latterdetermination the tube is presented to the specimen holder 2 in aposition so that the bar code does not interfere with the measurementprocess.

With respect to measuring gel level and height of fluid 26 above the gel24, the specimen is placed in a specimen holder 2 of FIG. 1, which willalso contain a linear array of LEDs 16 on one side of the tube, and acorresponding array of silicon detectors 20 on the opposite side of thetube. The LEDs 16 are coupled by electrical connections 6 to anelectronic driver 4. The detectors 20 are coupled by electricalconnections 7 to a microprocessor (not shown) which analyzes output. Thenumber of LEDs and detectors will depend on the length of the tube,e.g., for a commonly used tube of length 10 cm, 22 LEDs and 20 detectorsarranged 5 mm apart will be necessary to accommodate from a completelyfilled tube to an empty tube. In operation the first detector at the topof the column monitors as the three LED's opposite are flashed insuccession: one which is directly opposite, one 5 mm above, and one 5 mmbelow. The measured distance between the LEDs and the detectors is usedto determine tube diameter. This measurement is performedelectronically, mechanically or optically, or in any combination ofthese. In a preferred embodiment this measurement is performed by acombination of mechanical and electronic operations. The fluid volume iscalculated from the measured tube diameter and the measured height offluid above the gel barrier.

Alternatively, with respect to measuring gel level and height of fluid,a diode laser provides the radiation source wherein the source isfocused through a series of lenses 30 to spread the radiation 32 acrossthe length of the sample tube. The light being transmitted through thesample tube is passed through a further series of lenses 34 and directedonto a PDA sensor 36. Again, through this apparatus the tube is analyzedin 1 mm increments and the results are correlated to liquid height 26and gel level 24. It is readily apparent that either approach alsoallows for the determination of the hematocrit of any blood sample. Thisis achieved by centrifuging a whole blood sample in a container into twophases, one being the blood cells and the other being serum or plasma.The container is then scanned by the present invention and the length ofthe container that each of the phases occupies is thereby determined.With this data the ratio of the length amounts of the cellular phase andof the serum or plasma phase is converted to hematocrit value.

Based upon the results from the above determinations, the relativepositions of the tube and the fibre optics can be adjusted so as tooptimize the position of the fluid compartment for subsequentdeterminations. Consequently, there is space between the walls of thesample holder 2 and the fibre optics 10 and 14 to allow for suchadjustments.

With respect to determination of sample type, temperature, as well asfor measurement of interferents, reference is made to FIG. 2. The sample22 is placed into a specimen holder 2 (see FIG. 1 for longitudinal view)which is located in a housing (not shown). A radiation source 8, capableof emitting radiation in a range from about 400 nm to 2,500 nm, isoptically connected by fibre optics 10 to the sample. In operation whereabsorbance is measured the light source is directed through the sample,and the transmitted radiation is detected by a sensor 12, which is aphoto diode array (PDA), that is located opposite the source. Inoperation where reflectance is measured, the detectors are proximate tothe emission source (not shown). In both cases the detector is opticallyconnected by fibre optics 14, or any other suitable means. In thisapparatus the radiation source is split so that there is a referencebeam which bypasses the sample. The apparatus also contains a means forcorrelating a sensor response, from the sample path relative to a sensorresponse from the reference path, to a quantity of a known substance insaid sample. The housing has a cavity for receiving a sample and a lidfor selectively opening and closing the cavity. The radiation source isfor emitting a beam of radiation, and the sensor is responsive toreceipt of radiation.

While the invention has been particularly shown and described withreference to certain embodiments, it will be understood by those skilledin the art that various other changes in form and detail may be madewithout departing from the spirit and scope of the invention.

We claim:
 1. An apparatus for determining the hematocrit of a bloodsample said apparatus comprising: a) means for holding a specimencontainer wherein said means and said container have a longitudinalaxis; b) a radiation source disposed to direct radiation at saidspecimen and a radiation detector disposed to allow collection oftransmitted or reflected radiation from said specimen, said radiationsource comprising a linear array of LEDs disposed along one side of saidaxis of said container and said radiation detector comprising acorresponding array of silicon detectors on the opposite side of saidcontainer to collect transmitted radiation; c) electrical means tocouple said radiation source to an electronic driver; and d) electricalmeans to couple said radiation detector to a computing means whichanalyzes output from said detector for determination of hematocrit ofsaid sample.
 2. The apparatus of claim 1 further comprising one or morelenses to focus said radiation from said radiation source to spread saidradiation across said axis of said container, and further wherein saidApparatus contains one or more further lenses which collect transmittedor reflected radiation from said specimen and direct it to aspectrophotometric radiation detector.
 3. The apparatus of claim 1 or 2wherein said specimen container contains a sample identification labelon the exterior surface of said container.
 4. The apparatus of claim 1or 2 wherein said radiation is transmitted through a label, a containerand a sample.